Interesting fact:
Morihei Ueshiba, founder of Aikido, once pinned an opponent using only a single finger

OpponentOne who opposes in a disputation, argument, or other verbal controversy; specifically, one who attacks some thesis or proposition, in distinction from the respondent, or defendant, who maintains it."How becomingly does Philopolis exercise his office, and seasonably commit the opponent with the respondent, like a long-practiced moderator!"

Interesting fact:
Professional sumo wrestlers, called rikishi, must be quick on their feet and supple, but weight is vital to success as they hurl themselves at their opponents, aiming to floor them or push them outside the 15-foot fighting circle.

opponentSituated in front; opposite; standing in the way.

opponentOpposing; antagonistic; adverse.

opponentIn anatomy, bringing together or into opposition; having the action of an opponens. See opponens.

nopponentOne who opposes; an adversary; an antagonist; one who supports the opposite side in controversy, disputation, or argument, or in a contest of any kind.

nopponentOne who takes part in an opponency; the person who begins a dispute by raising objections to a tenet or doctrine: correlative to defendant or respondent. Synonyms Adversary, Antagonist, Opponent, etc. (see adversary), rival, competitor, opposer.

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Chambers's Twentieth Century Dictionary

Interesting fact:
President Grover Cleveland was a draft dodger. He hired someone to enter the service in his place, for which he was ridiculed by his political opponent, James G. Blaine. It was soon discovered, however, that Blaine had done the same thing himself.

adjOpponentō-pō′nent opposing in action, speech, &c.: placed in front

nOpponentone who opposes

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Quotations

Jan Christian Smuts

“A man is not defeated by his opponents but by himself.”

Sir James M. Barrie

“Never ascribe to an opponent motives meaner than your own.”

Cus D'Amato

“To see a man beaten not by a better opponent but by himself is a tragedy.”

Sam Snead

“Forget your opponents; always play against par.”

Don Piatt

“To be great one must be positive and gain strength from your opponents.”

Vince Lombardi

“Once you agree upon the price you and your family must pay for success, it enables you to ignore the minor hurts, the opponent's pressure, and the temporary failures.”

Etymology

Webster's Revised Unabridged Dictionary

L. opponens, -entis, p. pr. of opponere, to set or place against, to oppose; ob,see Ob-) + ponere, to place. See Position

Usage

In literature:

Furiously he flung himself into attacks on the classes from which his political opponents were drawn.

"Lloyd George" by Frank Dilnot

His opponent is likely to be overcautious.

"Infantry Drill Regulations, United States Army, 1911" by United States War Department

The French guns, however, had had the range and inflicted cruel losses on their opponents.

"Fighting in France" by Ross Kay

It was "catch as you can," and get your opponent down until both of his shoulders at the same time touch the ground.

"Three Boys in the Wild North Land" by Egerton Ryerson Young

So the wise man can never have an opponent; for whoever is able to face and find him has already gone over to his side.

"The Atlantic Monthly , Volume 2, No. 14, December 1858" by Various

He stood irresolute; while his opponent fixed his eye boldly on him.

"Ernest Bracebridge" by William H. G. Kingston

A brave man always appreciates the bravery of his opponent.

"Marmaduke Merry" by William H. G. Kingston

One after another, the British ships found themselves without opponents.

"True Blue" by W.H.G. Kingston

If Jackson was less confident than his opponents, he was not afraid.

"Expansion and Conflict" by William E. Dodd

Seeing this, our opponents became very brave.

"Travels and Adventures of Monsieur Violet" by Captain Marryat

No man was more dreaded by his opponents, more especially by those who had to encounter him while a contest was pending.

"The Story of the Upper Canada Rebellion, Volume 1" by John Charles Dent

Of Erik Trolle, another opponent of Sten Sture, we shall see more hereafter.

"The Swedish Revolution Under Gustavus Vasa" by Paul Barron Watson

Once seen and met by an opponent, he could never be forgotten.

"Scottish Football Reminiscences and Sketches" by David Drummond Bone

If the player's ball strike, or be moved by an opponent or an opponent's caddie or clubs, the opponent shall lose the hole.

"The Complete Golfer [1905]" by Harry Vardon

If unarmed, they would have met opponents also unarmed.

"History of Morgan's Cavalry" by Basil W. Duke

It was a form of attack to which their opponents exposed themselves by their faith in the utterly absurd stories of silly women.

"A History of Witchcraft in England from 1558 to 1718" by Wallace Notestein

The two brothers vanquish all opponents, but it is by claiming that the answer No does not preclude the answer Yes.

"Logic, Inductive and Deductive" by William Minto

He was sure that his immediate opponent was through, but there were others.

"Evil Out of Onzar" by Mark Ganes

He did not strike a blow, but simply stood up before his opponent with arms at guard.

"A Boy Knight" by Martin J. (Martin Jerome) Scott

The fall is won if an opponent touches the ground with his hand, knee, back, or side, as in the Cumberland and Westmorland style.

"Wrestling and Wrestlers:" by Jacob Robinson

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In poetry:

His opponents the laurel must certainly yield,
When he, with three legs, was equipp'd for the field;
For who could be better prepar'd for a fray?
With one he could fight, or with two run away.

"The Triumvirate" by William Hutton

Suet can draw a smile; and Farren
A coronet to put her hair in:
The powers of Erskine seldom fail
To make his opponent turn pale.
All who in rhetoric strain the throat,
Fade at the infant petticoat.

"The Valentine" by William Hutton

'I'll not surrender,' was his cry, 'before I do, I'll die!'
'All right,' his brave opponent said, 'now for it, you or I!'
A moment's pause - a parley now - the trooper made a push
To grapple at close quarters with the ranger of the bush.

"A Day's Ride" by Anonymous Oceania

My mates were strong and plucky chaps, but very soon I knew
That our opponents had the weight and strength to pull them through;
The boys were losing surely and defeat was very near,
When, high above the mighty roar, I heard the old man cheer!

"At the Tug-0-War" by Henry Lawson

Boodle battled strenuously, on his rival's ground encroaching;
Fearlessly the Foodle faction sneaked the other Party's views;
Full of fight were both opponents; the elections were approaching;
And upon mere Public Business none had any time to lose.

"Git-Yer-Gun" by C J Dennis

In news:

In 10 games this season, the Wolves have shut out their opponent five times.

Jaeland Lawson, not one to sleep well before big games — especially if he hates the opponent — simply went wild in the first half with 20 points as his Bearden Bulldogs built a 17-point lead at archrival Farragut.

In science:

The arrow arena is similar to the product arena but it involves the switching of polarities Proponent-Opponent for the arena in the contra-variant position, and extending the enabling relation so that initial moves of the argument are justiﬁed by the initial moves of the function.

The model of a term is a strategy, i.e. a set of plays indicating how the Proponent will respond to any Opponent action, given the play up to that point. A strategy is sub ject to certain closure conditions, which are not relevant for our discussion here.

In particular, under reasonable assumptions, if we give one player only O(log n) random coins but allow him to run in arbitrary polynomial time with nδ bits of randomness and we restrict his opponent to run in time nk , for some ﬁxed k, then we can sustain an ε-Nash equilibrium.

Repeated Matching Pennies with Limited Randomness

If this is the case, a Nash equilibrium can be viewed as a set of strategies in which each agent is simply computing his best response given his opponents’ actions.

Repeated Matching Pennies with Limited Randomness

In the repeated game, mixed strategies can be viewed as distribution over sequences of length n that are dependend on the opponent’s strategy.

Repeated Matching Pennies with Limited Randomness

To denote player’s i payoff we will sometimes use the standard notation E [U (Ri , R−i )], where Ri is player’s i mixed strategy and R−i is his opponent’s mixed strategy.

Repeated Matching Pennies with Limited Randomness

First notice that no player can improve his payoff in the ﬁrst n(1 − γ ) rounds, given his opponent’s strategy.

Repeated Matching Pennies with Limited Randomness

Notice that this deﬁnition implies that each agent can simulate any of his opponent’s strategies.

Repeated Matching Pennies with Limited Randomness

In this section we determine conditions under which a ε-Nash equilibrium can arise, given that one of the players has only a logarithmic amount of randomness and his opponent must run in time nk for some ﬁxed k .

Repeated Matching Pennies with Limited Randomness

This leads to a circular problem: we need to know the opponent’s intelligence ﬁrst in order to know the complexity of the problem.

On the influence of intelligence in (social) intelligence testing environments

The world will know who is who based on the acts of the opponent.

Comparison between the two definitions of AI

The player reaching this position wins; the opponent loses.

Multivision: an intractable impartial game with a linear winning strategy

In addition to the binary vectors Vi , also their true values (over the ring of integers) have to be maintained for checking the validity of the move of the opponent and for recognizing the end of the game.

Multivision: an intractable impartial game with a linear winning strategy

Her opponent will be called Antigeneric and will be referred to as “he”. (5) For a forcing notion P, ΓP stands for the canonical P–name for the generic ﬁlter in P.